1. Field of the Invention
The present invention relates generally to methods of forming fine patterns, and more particularly, to a method of forming patterns arranged in parallel with each other at very fine intervals and having a very fine width.
2. Description of the Background Art
FIGS. 38-41 are cross sectional views and perspective views showing a semiconductor device in each step in the order of a conventional method of forming fine patterns. The fine patterns include interconnection patterns, bit lines, word lines etc.
Referring to FIG. 38, a layer of object to be patterned (hereinafter referred to as object layer) 12 is formed on a support member 11 formed of a silicon dioxide film or the like. Object layer 12 is formed of polycrystalline silicon for example. Patterned resist 13 formed of novolak resin based positive photosensitive resin is formed on object layer 12.
Referring to FIG. 38 and 39, using patterned resist 13 as mask, object layer 12 is etched to remove the portion other than immediately below patterned resist 13 with a removing agent (such as bromine radical) 15 for removing the object layer, and patterns 12A, 12B, 12C and 12D of the object are formed.
Referring to FIGS. 40 and 41, patterned resist 13 is removed.
By the above-described method, patterns arranged in parallel to each other at intervals D and having a width W are provided as illustrated in FIG. 41.
A problem associated with the above method will be now described.
The width (W) of patterns 12A, 12B, 12C or 12D of the object provided according to the conventional method is determined by the pattern width of a light shielding film in the mask used (in the case of using positive photoresist) or the distance between light shielding films (in the case of using negative photoresist). Therefore fine patterns having a width and a size as small as or smaller than the minimum resolution achieved by lithography cannot be formed. In other words, the pattern width (W) and pattern distance (D) are each at least 0.25 .mu.m, and fine patterns having pattern width (W) and distance (D) smaller than this size cannot be formed.
FIGS. 42A-42F are cross sectional views showing a semiconductor device in each step in the order of a method of forming fine patterns according to a prior art (Japanese Patent Laying-Open No. 2-5522) related to the present invention.
Referring to FIG. 42A, resist 2 is formed on a support member 1.
Referring to FIG. 42B, resist 2 is selectively irradiated with a ultraviolet beam, and a latent image 3 is formed.
Referring to FIGS. 42B and 42C, developing resist 2 forms patterned resist 13.
Referring to FIG. 42D, a silylated layer 13a is formed on a surface of patterned resist 13 by irradiating support member 1 with a ultraviolet beam in vapor of hexamethyldisilazane (HMDS). Referring to FIGS. 42D and 42E, silylated layer 13a formed on the top surface of patterned resist 13 is removed by means of reactive ion etching.
Referring to FIGS. 42E and 42F, the not silylated portion of resist 13 is etched away. Thus, fine patterns 16a are formed.
According to the conventional technique, however, a reaction chamber for reacting the photosensitive resin and HMDS must be improved such that a far ultraviolet beam can be introduced into the reaction chamber, which complicates the device and pushes up the cost.